FIGS. 1 to 3 are schematic plan view of the main portion of a conventional cassette loading mechanisms the cassette loading mechanism is illustrated in a series of modes of operation from a position in which a cassette is being inserted and to a position in which the cassette is displaced to a mounted position through a push-in position. In the figures, a recording medium cassette 1 containing a magnetic tape, for example, is provided with a slider for opening and closing the cover (not illustrated). A cassette holder 2 having a box-shaped cross section for holding the cassette 1 is best illustrated in FIG. 4. The leading edge of the cassette holder 2 has a pair of pawls 2a for engaging and shifting the slider on the cassette 1. Guide pins 3 are planted at both sides of the cassette holder 2. A frame 4 is of a U-shaped cross section having guide holes (not shown) in the respective side portions 4a for guiding the guide pins 3. A detecting member 5 (lever) is pivotally supported about the shaft 6 at the deeper side of the frame 4, having an arc portion 5A exhibiting a cam function and an engaging portion engageable with the cassette 1. A spring biasing means 7 is disposed between the frame 4 and the lever 5 for biasing the lever 5 into an inoperated position. A detection element 8 (start switch) is disposed in the vicinity of a corner portion of the arc 5A of the lever 5 to be activated in accordance with the movement of the lever 5 for controlling the cassette loading mechanism.
In the conventional cassette loading mechanism of the above construction, when the cassette 1 is inserted into the cassette holder 2 in the direction of an arrow A, the slider of the cassette 1 engages the pawls 2a of the cassette holder 2 to move the slider into a released position, so that the cassette is brought into a position in which its cover can be opened. In this position, since the leading edge of the cassette 1, as viewed in the direction of insertion, does not rotate the tip of the lever 5, the cassette 1 is held within the cassette holder 2 without activating the start switch 8 (detection element). This position is referred to as a cassette insertion position.
Then, when the cassette 1 is further pushed forward from the insertion position shown in FIG. 1, in the direction of the arrow A, the cassette 1 is moved against the biasing force of the spring (not shown) biasing the cassette holder 2 in the direction opposite to the direction of insertion of the cassette 1. Thus, in the push-in position illustrated in FIG. 2 in the cassette 1 is pushed within the cassette loading mechanism together with the cassette holder 2 beyond the insertion position illustrated in FIG. 1. In this position, the leading edge of the cassette 1 pushes the engagement portion of the lever 5 to rotate the lever 5 clockwise and the start switch 8 is switched to the actuated position by the cam surface 5A of the lever 5.
Thus, the start switch 8 detects that the rotational position of the lever 5 or the position of the cassette 1 is changed the insertion position to the pushed-in position, upon which a drive unit (not illustrated) is energized to move the cassette holder 2 with the cassette 1 therein deep into the frame 4 until it reaches the predetermined mount position illustrated in FIG. 3. When the cassette holder 2 is being placed in the mount position, it is moved in the direction from the front side to the back side plane of the figure. The cover (not shown) of the cassette 1 is opened during the above movement.
In the conventional cassette loading mechanism of the above construction, the detection of the position of the cassette is achieved by causing the single engagement portion of the lever 5 of the detection member to engage the central portion of the leading edge of the cassette 1. The cassette 1 is arranged to be moved to a predetermined mounted position on the basis of the results of such detection. However, even when the cassette 1 is inserted at a skewed position with respect to the cassette holder 2 as illustrated in FIG. 5, the corner portion 1a of the cassette 1 abuts the tip portion of the lever 5 and rotates it. This rotation is detected by the start switch 8 and the drive unit for driving the cassette holder 2 toward the predetermined mounted position is energized with the cassette 1 not properly inserted. When the cassette 1 and the cassette holder 2 are moved under such conditions, they interfere with the components of the cassette loading mechanism during the movement, thus disadvantageously damaging the mechanism and the cassette 1.